1. Field of the Invention
The present invention relates to a many-headed grinding machine such as a double-headed grinding machine to be adapted, for example, when grinding a pin of a clunk shaft for an engine and a grinding method using the many-headed grinding machine.
2. Description of the Related Art
According to the double-headed grinding machine, by simultaneously bring grinding wheels into contact with two processing places on a longitudinal work respectively while supporting the work between a pair of spindle stocks and rotating the work around its axis, outer circumferential faces of these processing places are ground and processed simultaneously. Then, grinding due to a plurality of grinding machines is carried out sequentially through a plurality of grinding steps such as rough grinding, middle grinding, and finishing grinding having different work rotation rate and different process feeding rate.
However, processing end timings in the above-described respective grinding steps may be varied due to a difference in flexure of the work and the sharpness of respective grinding wheels. Accordingly, in such a case, if the grinding processing of one grinding wheel is finished, the grinding processing is carried out only by other grinding wheel. Then, after the grinding processing due to the former grinding wheel is finished, the grinding is carried out only by one grinding wheel, so that a balance of grinding load added to the work becomes unstable and accuracy of processing is remarkably lowered.
In order to solve such a problem, in a patent document 1 (JP-A-2003-136379), the invention such that the last grinding processing of the work due to a pair of grinding wheels are carried out simultaneously has been proposed. According to the invention disclosed in this patent document 1, upon grinding processing of a plurality of places on the longitudinal work by using a plurality of grinding wheels, the outer circumferential measurement if each processing place of the work is measured. Then, on the basis of this measurement, a plurality of grinding wheels is controlled to be driven. In other words, as shown in FIG. 12, when a measurement value (the outer circumferential method of the work) at the processing portion of the former grinding processing is made into a predetermined value d, the cutting of this former processing portion is stopped. Then, till the measurement value at the processing portion of the following grinding processing is made into the predetermined value d, the cutting of the former processing portion is awaited, and when the measurement values of the former and following processing portions coincide with each other, the cutting of the both are restarted at the same time to start the last precision grinding step.
[Patent document 1] JP-A-2003-136379
According to the invention in the above-described patent document 1, by starting the last grinding steps simultaneously, the processing precision can be improved, however, even when one grinding wheel stops the feeding since it awaits other grinding wheel, the work contacts the grinding wheel via a grinding liquid and the cutting of the work may proceed with the work pressed against the grinding wheel by its elastic recovery or the like. Therefore, even if the last grinding step is carried out, necessary precision may not be acquired at one processing portion and imbalance is caused between the processing portions of the work. In order to prevent the cutting from proceeding at the side where the processing feeding stops, it may be possible that the grinding wheel is separated from the work, however, in such a case, it is feared that the imbalance becomes larger due to bringing the grinding wheel into contact with the work again.